The present invention relates to an ink jet printer, in which a printing head arranging a plurality of nozzles in a line is mounted on the carriage moved relative to the recording medium, in such a manner that the printing head is inclined by a predetermined angle with respect to the printing direction, and those nozzles are operated successively at predetermined time intervals to jet ink, thereby to print in the direction of an arrangement of the nozzles and by a length of the arrangement of the nozzles, i.e., one printing line. More particularly, the present invention relates to the ink jet printer which is allowed to correct a shift in position while printing (hereinafter referred to as "a printing shift", when applicable), which is due to the mounting angle error generated when the printing head is mounted on the carriage.
Japanese Patent Application (OPI) No. 138953/1982 (the term "OPI" as used herein means an "unexamined published application") discloses a multi-ink jet printer in which a plurality of nozzles arranged in a line are mounted on the carriage moved relative to the recording medium in such a manner that the nozzles are inclined by a predetermined angle with respect to the printing direction. More specifically, the printing head of the ink jet printer has a plurality of nozzles set in such a manner that the nozzles are arranged in a line and inclined by a predetermined angle .theta..degree. with respect to the printing direction as shown in the FIG. 3(a), and is mounted on the carriage which is moved relative to the recording medium. Each of the nozzles is operated successively at a predetermined time interval t (sec) one by one, thereby to jet ink, and print in the direction of the arrangement of the nozzles and by a length thereof.
On the other hand, in order to correct the printing shift which occurs at a printing boundary between adjacent scanning lines, Japanese Patent Application (OPI) No's 109657/1987 and 243374/1990 disclose a method in which a test printing operation is carried out several times by moving the carriage both in "go" and "return" modes, and then an optimum printing position is determined by correcting the printing shift in each of the two modes.
However, in the case that a high-resolution printing head or a printing head having a large number of nozzles is used to obtain a high quality image, it cannot disregard a mounting angle error generated when the printing head is mounted on the carriage, so that there is a problem that the printed record is inclined without being printed vertical to the movement direction of the carriage.
The inclination of the printed record, which is due to the mounting angle error of the printing head, cannot be corrected by the aforementioned methods. Furthermore, with the ink jet printer, a printing shift occurs at the printing boundary. Therefore, the resultant record is greatly deteriorated in image quality. In the test printing method as described above, the test printing operation is carried out several times in a reciprocation mode until the printing shift is eliminated. If the printing shift is greatly generated, then the test printing operation must be carried out so many times. On the other hand, with an ink jet printer in which the carriage is driven at two different speeds such as a normal speed and a higher speed, the printing position determined by the test printing method cannot be applied as it is. Particularly, since the printing position is determined without taking the variation of the carriage driving speed into account, there is a problem that the printing shift is generated at the printing boundary.